(1) Field of the Invention
The present invention relates to methods used to fabricate semiconductor devices, and more specifically to a method used to fabricate a capacitor under bit line (CUB), dynamic random access memory (DRAM), device.
(2) Description of Prior Art
As the density of DRAM cells increase, the dimensions of the DRAM device has to be decreased. The decreasing size of a specific DRAM device adversely influences the ability to provide the needed DRAM capacitance. Increasing the vertical dimensions for DRAM, crown shaped capacitor structures have allowed the desired capacitance values for DRAM devices to be achieved. The increase in these vertical dimensions is usually accomplished via formation of the crown shaped capacitor structure, located in capacitor openings, and in turn formed in thick insulator layers. However the use of thick insulator layer for the capacitor openings, result in high aspect ratio for bit line contact holes, used in for capacitor over bit line (CUB), designs. The additional thickness of insulator, needed to increase the vertical dimension of the crown shaped capacitor structure, results in difficulties when anisotropically dry etching a narrow diameter, deep, opening, to expose a bit line region.
This invention will describe a novel process sequence in which the desired increase in the vertical dimensions of the crown shaped capacitor structure is achieved via formation of the capacitor openings in thicker insulator layers, however without increasing the aspect ratio for the dry etched, narrow diameter bit line contact hole. Prior art, such as Tu et al, in U.S. Pat. No. 6,100,129, as well as Chen et al, in U.S. Pat. No. 6,077,742, describe methods of fabricating DRAM crown shaped capacitor structures. These prior arts however do not describe the novel process sequence of this present invention, where a CUB DRAM device is fabricated with increased capacitance, as a result of increased vertical, crown shaped features, without increasing the aspect ratio of the bit line contact hole opening.